// return stack
       Reg#(State_t) rs[3];

       for (int i = 0; i < 3; i = i + 1)
          rs[i] <- mkRegU;

`define call(SUB)        `_pushNext; state <= State_t {func:SUB, step:S0}
`define _pushNext        rs[sp] <= State_t {func:state.func, step:nextStep()}; sp <= sp + 1
`define return           state <= rs[sp-1]; sp <= sp - 1
`define next             state.step <= nextStep()

$ bsc -sim -u TestFSM4.bsv
checking package dependencies
compiling TestFSM3.bsv
code generation for mkTestFSM starts
Elaborated module file created: mkTestFSM.ba
All packages are up to date.
$ bsc -sim -e mkTestFSM -o mkTestFSM
Bluesim object created: mkTestFSM.{h,o}
Bluesim object created: model_mkTestFSM.{h,o}
Simulation shared library created: mkTestFSM.so
Simulation executable created: mkTestFSM
$ ./mkTestFSM -m 15 -V dump.vcd | tee result
L1 S0
L1 S1
　L2 S0
　L2 S1
　L2 S2
　　L3 S0
　　L3 S1
　　　L4 S0
　　　L4 S1
　　L3 S2
　L2 S3
　L2 S4
L1 S2
L1 S2
$